Compilare: user.cpp: In function ‘int main()’: user.cpp:32:56: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (i = 0; i + a.size() <= b.size() && i < b.size() && x.size() < 1000; i++) ^ user.cpp:37:11: warning: statement has no effect [-Wunused-value] for (i; i + a.size() <= b.size() && i < b.size(); i++) ^ user.cpp:37:52: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (i; i + a.size() <= b.size() && i < b.size(); i++) ^